Tire CodeExplanation

Tire code or Tyre code -
Automobiletires
are described by an alphanumeric code, which is generally
molded into the
sidewall of the tire. This code specifies the dimensions of
the tire, and some of its key limitations, such as load-bearing
ability, and maximum speed. Sometimes the inner sidewall
contains information not included on the outer sidewall, and
vice versa.

The code has grown in complexity over the years, as is
evident from the mix of metric and imperial units, and ad-hoc
extensions to lettering and numbering schemes. New automotive
tires frequently have ratings for traction, treadwear, and
temperature resistance (collectively known as
The
Uniform Tire Quality Grade (UTQG) ratings).

Most tires sizes are given using the ISO Metric sizing
system. However, some
pickup trucks and
SUVs use the Light Truck Numeric or Light Truck High
Flotation system.

The
ISO Metric tire code consists of a string of letters and
numbers, as follows:

An optional letter (or letters) indicating the intended
use or vehicle class for the tire:

P: Passenger Car

LT: Light Truck

ST: Special Trailer

T: Temporary (restricted usage for
"Space-Saver" spare wheels)

3 digit number: The "nominal section width" of
the tire in millimeters; the widest point from both outer
edges.

/: Slash character

2 or 3 digit number: The "aspect ratio" of the
sidewall height to the total width of the tire, as a
percentage. If this is missing, it is assumed to be 82%. If
the number is larger than 200, then this is the diameter of
the entire tire in millimeters.

An optional letter indicating construction of the fabric
carcass of the tire:

B: bias belt (where the sidewalls are the
same material as the tread, leading to a rigid ride)

2 digit number: Diameter in inches of the wheel
that the tire is designed to fit

2 or 3 digit number: Load index; see table below

1 or 2 digit/letter combo: Speed rating; see
table below

Additional marks: See subheading below.

Light Trucks

Some light truck tires follow the Light Truck Numeric or
Light Truck High Flotation systems, indicated by the letters LT
at the end instead of the beginning of the sequence, as follows:

The tire diameter is given for High Flotation tires and
omitted from Numeric tires.

2 digit number: The diameter of the tire in
inches.

x: Separator character.

3 or 4 digit number: The section width (cross
section) of the tire in inches. If the tire diameter is not
given, section widths ending in zero (e.g., 7.00 or 10.50)
indicate the aspect ratio is 92%, while section widths not
ending in zero (e.g., 7.05 or 10.55) indicate the aspect
ratio is 82%.

Construction of the fabric of the tire:

B: bias belt

D: diagonal

R: radial

2 digit number: Diameter in inches of the rim
that this tire is designed to fit.

LT: Designates that this is a Light Truck tire.

Load index and speed rating are not required for this
type of tire but may be provided by the manufacturer.

Load Range

Speed rating

The code is made up of one or two letters, or one letter and
one number. It indicates the maximum permitted speed that the
tire can sustain for a ten minute endurance without being in
danger

Speed rating

Code

mph

km/h

Code

mph

km/h

A1

3

5

L

75

120

A2

6

10

M

81

130

A3

9

15

N

87

140

A4

12

20

P

94

150

A5

16

25

Q

100

160

A6

19

30

R

106

170

A7

22

35

S

112

180

A8

25

40

T

118

190

B

31

50

U

124

200

C

37

60

H

130

210

D

40

65

V

149

240

E

43

70

Z

over 149

over 240

F

50

80

W

168

270

G

56

90

(W)

over 168

over 270

J

62

100

Y

186

300

K

68

110

(Y)

over 186

over 300

Prior to 1991, tire speed ratings were shown inside the tire
size, before the "R" character. The available codes were SR
(112 mph, 180 km/h), HR (130 mph, 210 km/h), VR (in excess of
130 mph, 210 km/h) and ZR (in excess of 149 mph, 240 km/h). The
ZR code is still in common use, often combined with a W or Y
speed code.

Tires with a speed rating higher than 186 mph (300 km/h) are
indicated by a Y in parenthesis The load rating is often
included within the parenthesis, e.g. (86Y).

In many countries, the law requires that tires must be
specified, and fitted, to exceed the maximum speed of the
vehicle they are mounted on, with regards to their speed rating
code (except for "Temporary Use" spare tires). In
Germany, tires that are not fit for a car's or motorcycle's
particular maximum speed are illegal to mount, unless a warning
sticker stating the allowed maximum speed is placed within clear
sight of the driver inside the vehicle. Some manufacturers will
install a
speed governor if a vehicle is ordered with tires rated
below the vehicle's maximum speed.

If a tire is replaced with a lower speed rating than
originally specified by the vehicle manufacturer, then this may
render the vehicle insurance invalid.

Tires marks

There are numerous other markings on a typical tire, these
may include:

M+S, or M&S: Mud and Snow; all-weather
tires, with above-average traction in muddy or very light
snowy conditions, and for low ambient temperatures. Not a
winter tire unless it has the snowflake and mountain symbol.
Spike tires have an additional letter, "E" (M+SE).

BSW: Black SideWall

WSW: White SideWall

OWL: Outline White Lettering

E4: Tire approved according ECE-regulations, the
number indicating the country of approval.

030908: Approval number of the tire

DOT code: All tires for use in the USA have the
DOT code, as required by the
Department of Transportation (DOT). It specifies the
company, factory, mold, batch, and date of production (2
digits for week of the year plus 2 digits for year; or 2
digits for week of the year plus 1 digit for year for tires
made prior to 2000). Although not law, tire manufacturers do
not suggest using a "new" tire that has been sitting on the
shelf for more than 6 years.

TWI: Tread Wear Indicator; a device, such as a
triangle or a small
Michelin Man icon, located where the tread meets the
sidewall. It indicates the location of the raised wear bars
in between the tire tread channels.

SL: Standard Load; tire for normal usage and
loads

XL: eXtra Load; tire for vehicles of heavier
standard weights

RF: Reinforced tires

Arrows: Some tread designs are "directional", and
designed to perform better when driven in a specific
direction (clockwise or counter-clockwise). Such tires will
have an arrow showing which way the tire should rotate when
the vehicle is moving forwards. It is important not to put a
"clockwise" tire on the left hand side of the car or a
"counter-clockwise" tire on the right side.

To facilitate proper balancing, most high performance
tire manufacturers place laso red (uniformity) and yellow
(weight) dots - marks on the sidewalls of its tires to
enable the best possible match-mounting of the tire/wheel
assembly.[2]

Tire geometry

When referring to the purely geometrical data, a shortened
form of the full notation is used. To take a common example,
195/55R16 would mean that the nominal width of the tire is
approximately 195 mm at the widest point, the height of the
side-wall of the tire is 55% of the width (107 mm in this
example) and that the tire fits 16 inch diameter wheels. The
code gives a direct calculation of
diameter.

Less commonly used in the USA and Europe (but often in Japan
for example) is a notation that indicates the full tire diameter
instead of the side-wall height. To take the same example, a
16 inch wheel would have a diameter of 406 mm. Adding twice the
tire height (2×107 mm) makes a total 620 mm tire diameter.
Hence, a 195/55R16 tire might alternatively be labelled
195/620R16.

Whilst this is theoretically ambiguous, in practice these two
notations may easily be distinguished because the height of the
side-wall of an automotive tire is typically much less than the
width. Hence when the height is expressed as a percentage of the
width, it is almost always less than 100% (and certainly less
than 200%). Conversely, vehicle tire diameters are always larger
than 200 mm. Therefore, if the second number is more than 200,
then it is almost certain the Japanese notation is being used—if
it is less than 200 then the U.S./European notation is being
used.